RE: Average amount of meat after processing?
Jen approx. 1/3 of live weight will transpire to boned out meat for the freezer. In your case you'd be looking at a live weight animal of about 85lbs which would only be a few punds heavier than last years animal...so if you think it weighted 30 pounds heavier your meat take should have been 10 pounds more at 38lbs. Again some deer are more and some are less really depends on the individual deer but this would get you close.
As to shooting in the guts, won't ruin much meat. The only thing you'll ruin on a stomach in and out shot is flank and some intercostal rib meat, which amounts to very little in total make up a deer carcass/meat you get. However if you got the deer in the backstraps that can account for a lot of meat loss.
My best advice is do it yourself, than you know your getting what you got. It ain't that hard and plenty of books, videos and people here that will help you out in getting started.